
import {
    Blob,
    btoa,
    createImageBitmap,
    CSSStyleDeclaration,
    performance,
    document,
    DOMParser,
    EventTarget,
    fetch,
    Headers,
    HTMLCanvasElement,
	Image,
    HTMLImageElement,
    ImageBitmap,
    location,
    navigator,
    Request,
    requestAnimationFrame,
    cancelAnimationFrame,
    Response,
    URL,
    window,
    self,
    WebAssembly,
    Worker,
    XMLHttpRequest,
	ImageData,
	TextDecoder,
    core
    } from 'dhtml-weixin';
import {
	ShaderNode, div, max, sub, mul, clamp, pow, pow2, pow4, cond, greaterThan
} from '../../shadernode/ShaderNodeBaseElements.js';

const getDistanceAttenuation = new ShaderNode( ( inputs ) => {

	const { lightDistance, cutoffDistance, decayExponent } = inputs;

	// based upon Frostbite 3 Moving to Physically-based Rendering
	// page 32, equation 26: E[window1]
	// https://seblagarde.files.wordpress.com/2015/07/course_notes_moving_frostbite_to_pbr_v32.pdf
	const distanceFalloff = div( 1.0, max( pow( lightDistance, decayExponent ), 0.01 ) );

	return cond(
		greaterThan( cutoffDistance, 0 ),
		mul( distanceFalloff, pow2( clamp( sub( 1.0, pow4( div( lightDistance, cutoffDistance ) ) ) ) ) ),
		distanceFalloff
	);

} ); // validated

export default getDistanceAttenuation;
